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[DO] Updating code for websocket hibernation #24234

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merged 2 commits into from
Aug 7, 2025
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[DO] Updating code for websocket hibernation #24234

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Updating code for websocket hibernation
Oxyjun Aug 7, 2025
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Changing 4-space indentation to 2-space indentation
Oxyjun Aug 7, 2025
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196 changes: 121 additions & 75 deletions src/content/docs/durable-objects/examples/websocket-hibernation-server.mdx
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Expand Up @@ -24,88 +24,134 @@ WebSocket Hibernation is unavailable for outgoing WebSocket use cases. Hibernati

<TypeScriptExample>
```ts
import { DurableObject } from "cloudflare:workers";

export interface Env {
WEBSOCKET_HIBERNATION_SERVER: DurableObjectNamespace<WebSocketHibernationServer>;
}
import { DurableObject } from 'cloudflare:workers';

// Worker
export default {
async fetch(
request: Request,
env: Env,
ctx: ExecutionContext,
): Promise<Response> {
if (request.url.endsWith("/websocket")) {
// Expect to receive a WebSocket Upgrade request.
// If there is one, accept the request and return a WebSocket Response.
const upgradeHeader = request.headers.get("Upgrade");
if (!upgradeHeader || upgradeHeader !== "websocket") {
return new Response("Durable Object expected Upgrade: websocket", {
status: 426,
});
}

// This example will refer to the same Durable Object,
// since the name "foo" is hardcoded.
let id = env.WEBSOCKET_HIBERNATION_SERVER.idFromName("foo");
let stub = env.WEBSOCKET_HIBERNATION_SERVER.get(id);

return stub.fetch(request);
}

return new Response(null, {
status: 400,
statusText: "Bad Request",
headers: {
"Content-Type": "text/plain",
},
});
},
async fetch(request: Request, env: Env, ctx: ExecutionContext): Promise<Response> {
if (request.url.endsWith('/websocket')) {
// Expect to receive a WebSocket Upgrade request.
// If there is one, accept the request and return a WebSocket Response.
const upgradeHeader = request.headers.get('Upgrade');
if (!upgradeHeader || upgradeHeader !== 'websocket') {
return new Response('Worker expected Upgrade: websocket', {
status: 426,
});
}

if (request.method !== 'GET') {
return new Response('Worker expected GET method', {
status: 400,
});
}

// Since we are hard coding the Durable Object ID by providing the constant name 'foo',
// all requests to this Worker will be sent to the same Durable Object instance.
let id = env.WEBSOCKET_HIBERNATION_SERVER.idFromName('foo');
let stub = env.WEBSOCKET_HIBERNATION_SERVER.get(id);

return stub.fetch(request);
}

return new Response(
`Supported endpoints:
/websocket: Expects a WebSocket upgrade request`,
{
status: 200,
headers: {
'Content-Type': 'text/plain',
},
}
);
},
};

// Durable Object
export class WebSocketHibernationServer extends DurableObject {
async fetch(request: Request): Promise<Response> {
// Creates two ends of a WebSocket connection.
const webSocketPair = new WebSocketPair();
const [client, server] = Object.values(webSocketPair);

// Calling `acceptWebSocket()` informs the runtime that this WebSocket is to begin terminating
// request within the Durable Object. It has the effect of "accepting" the connection,
// and allowing the WebSocket to send and receive messages.
// Unlike `ws.accept()`, `state.acceptWebSocket(ws)` informs the Workers Runtime that the WebSocket
// is "hibernatable", so the runtime does not need to pin this Durable Object to memory while
// the connection is open. During periods of inactivity, the Durable Object can be evicted
// from memory, but the WebSocket connection will remain open. If at some later point the
// WebSocket receives a message, the runtime will recreate the Durable Object
// (run the `constructor`) and deliver the message to the appropriate handler.
this.ctx.acceptWebSocket(server);

return new Response(null, {
status: 101,
webSocket: client,
});
}

async webSocketMessage(ws: WebSocket, message: ArrayBuffer | string) {
// Upon receiving a message from the client, the server replies with the same message,
// and the total number of connections with the "[Durable Object]: " prefix
ws.send(
`[Durable Object] message: ${message}, connections: ${this.ctx.getWebSockets().length}`,
);
}

async webSocketClose(
ws: WebSocket,
code: number,
reason: string,
wasClean: boolean,
) {
// If the client closes the connection, the runtime will invoke the webSocketClose() handler.
ws.close(code, "Durable Object is closing WebSocket");
}
// Keeps track of all WebSocket connections
// When the DO hibernates, gets reconstructed in the constructor
sessions: Map<WebSocket, { [key: string]: string }>;

constructor(ctx: DurableObjectState, env: Env) {
super(ctx, env);
this.sessions = new Map();

// As part of constructing the Durable Object,
// we wake up any hibernating WebSockets and
// place them back in the `sessions` map.

// Get all WebSocket connections from the DO
this.ctx.getWebSockets().forEach((ws) => {
let attachment = ws.deserializeAttachment();
if (attachment) {
// If we previously attached state to our WebSocket,
// let's add it to `sessions` map to restore the state of the connection.
this.sessions.set(ws, { ...attachment });
}
});

// Sets an application level auto response that does not wake hibernated WebSockets.
this.ctx.setWebSocketAutoResponse(new WebSocketRequestResponsePair('ping', 'pong'));
}

async fetch(request: Request): Promise<Response> {
// Creates two ends of a WebSocket connection.
const webSocketPair = new WebSocketPair();
const [client, server] = Object.values(webSocketPair);

// Calling `acceptWebSocket()` informs the runtime that this WebSocket is to begin terminating
// request within the Durable Object. It has the effect of "accepting" the connection,
// and allowing the WebSocket to send and receive messages.
// Unlike `ws.accept()`, `this.ctx.acceptWebSocket(ws)` informs the Workers Runtime that the WebSocket
// is "hibernatable", so the runtime does not need to pin this Durable Object to memory while
// the connection is open. During periods of inactivity, the Durable Object can be evicted
// from memory, but the WebSocket connection will remain open. If at some later point the
// WebSocket receives a message, the runtime will recreate the Durable Object
// (run the `constructor`) and deliver the message to the appropriate handler.
this.ctx.acceptWebSocket(server);

// Generate a random UUID for the session.
const id = crypto.randomUUID();

// Attach the session ID to the WebSocket connection and serialize it.
// This is necessary to restore the state of the connection when the Durable Object wakes up.
server.serializeAttachment({ id });

// Add the WebSocket connection to the map of active sessions.
this.sessions.set(server, { id });

return new Response(null, {
status: 101,
webSocket: client,
});
}

async webSocketMessage(ws: WebSocket, message: ArrayBuffer | string) {
// Get the session associated with the WebSocket connection.
const session = this.sessions.get(ws)!;

// Upon receiving a message from the client, the server replies with the same message, the session ID of the connection,
// and the total number of connections with the "[Durable Object]: " prefix
ws.send(`[Durable Object] message: ${message}, from: ${session.id}. Total connections: ${this.sessions.size}`);

// Send a message to all WebSocket connections, loop over all the connected WebSockets.
this.sessions.forEach((attachment, session) => {
session.send(`[Durable Object] message: ${message}, from: ${attachment.id}. Total connections: ${this.sessions.size}`);
});

// Send a message to all WebSocket connections except the connection (ws),
// loop over all the connected WebSockets and filter out the connection (ws).
this.sessions.forEach((attachment, session) => {
if (session !== ws) {
session.send(`[Durable Object] message: ${message}, from: ${attachment.id}. Total connections: ${this.sessions.size}`);
}
});
}

async webSocketClose(ws: WebSocket, code: number, reason: string, wasClean: boolean) {
// If the client closes the connection, the runtime will invoke the webSocketClose() handler.
ws.close(code, 'Durable Object is closing WebSocket');
}
}
```
</TypeScriptExample>
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